1. Field of the Invention
This invention relates to a connection on the rotor of a helicopter where rotor blades are joined to a hub for articulated movement. More particularily the invention pertains to a bearing located at the connection that permits universal rotation of blades with respect to the hub and integrally damps rotational movement about intersecting axes.
2. Description of the Prior Art
U.S. Pat. No. 3,106,965 describes a helicopter rotor having a universal bearing comprising spherical, axially spaced concentric members having a body of alternating laminates of elastomer and metal bonded to the members. Centrifugal force carried along the rotor blades is transmitted through the bearing by compressing the body of laimates. Motion of the blade about perpendicular axes intersecting at the bearing center is limited by elastomeric stops that prevent lead-lag and flapping movement of the rotor due to contact with the stops. Damping is contolled by varying the elastomer from which the stops are fabricated.
U.S. Pat. No. 4,588,356 describes use of multiple elastomeric bearings in a rotor head. One of the bearings, located between a fork element and hub, damps blade oscillation in the verticle and horizontal planes. Damping capacity of the bearing is adjustable by varying radii of curvature of faces whose centers coincide with a virtual hinge, about which the blades oscillate in the hub plane.
U.S. Pat. No. 4,732,540 describes a technique for restraining non-rotational flapwise movement of a helicopter rotor blade mounted on a rotor that employs a spherical bearing comprising a stack of metal and synthetic rubber laminates retained between rigid frames. In-plane damping results from operation of a drag damper operating between an attachment on the blade, located outboard of the bearing, and a clevis attachment on the rotor hub. The damper is a cylindrical sleeve of visco-elastic material joined by ball and socket connections to blade and hub.
The drag dampers described in U.S. Pat. No. 4,749,339 are conventional hydraulic devices, an alternating stack of rigid plates and plates, or coaxial tubes having a cylindrical sleeve of visco-elastic material located between the tubes.